Super-sensitized photographic silver halide emulsions

ABSTRACT

SENSITIVITY IS INCREASED MARKEDLY WITHOUT ACCOMPANYING INCREASED FOG FORMATION BY SUPER-SENSITIZING A PHOTOGRAPHIC SILVER HALIDE EMULSION CONTAINING A SENSITIZING CYANINE DYE WITH A QUATERNARY SALT OF IMIDAZOLE SHOWN BY THE GENERAL FORMULA:   1-R1,2-R,3-R2,4-Y2,5-Y1-IMIDAZOLIUM X(-)(N-1) OR   1-R1,2-R,3-((1-R3,2-R,4-Y2,5-Y1-IMIDAZOL-3-YL)-(CH2)M-),4-   Y2,5-Y1-IMIDAZOLINIUM 2X(-)   WHEREIN R IS H, AN ALKYL GROUP, OR A HYDROXYALKL GROUP, EACH OF R1 AND R2 IS AN ALKYL, ARALKYL, HYDROXYALKYL, ACETOXYALKYL, ARYL, OR ALKENYL GROUP, X IS AN ANION, EACH OF Y1 AND Y2 IS H, AN ALKYL GROUP OR A HALOGEN ATOM.

United States Patent Oflice 3,592,654 Patented July 13, 1971 US. Cl. 96-126 12 Claims ABSTRACT OF THE DISCLOSURE Sensitivity is increased markedly without accompanying increased fog formation by super-sensitizing a photographic silver halide emulsion containing a sensitizing cyanine dye with a quaternary salt of imidazole shown by the general formula:

wherein R is H, an alkyl group, or a hydroxyalkyl group, each of R and R is an alkyl, aralkyl, hydroxyalkyl, acetoxyalkyl, aryl, or alkenyl group, X is an anion, each of Y and Y is H, an alkyl group or a halogen atom.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a dye-sensitized photographic silver halide emulsion and more particularly to a so-called super sensitizer photographic silver halide emulsion.

(2) Description of the prior art It is well known in the field of producing photographic silver halide emulsions that by adding a sensitizing dye to a silver halide emulsion, the range of light-sensitive wavelength of the silver halide emulsion is enlarged, that is, the silver halide emulsion is optically sensitized. Further, it is known that by incorporating a colorless compound in the optically sensitized silver halide emulsion, light sensitivity at a definite range of light sensitive wavelength is increased.

The thus obtained eifect is known as super sensitization. On the other hand, hyper-sensitization, in which the light sensitivity is found over the whole range of lightsensitive Wavelengths, has the disadvantage that, since the light sensitivity is increased by processing of the finally obtained photographic light sensitive films or plates (usually pAg is decreased and pH is increased by the processing), the preservability of the light sensitive materials is lowered.

Therefore, an object of the invention is to provide a super dye sensitized photographic silver halide emulsion having a good preservability. Another object of this invention is to provide a photographic silver halide emulsion containing a sensitizing cyanine dye super-sensitized by a quaternary salt of an imidazole without increasing fog formation.

SUMMARY OF THE INVENTION The inventors have found that the above object of this invention can be achieved by incorporating in a photographic silver halide emulsion optically sensitized by a cyanine dye at least one quaternary salt of an irnidazole represented by the following general Formula I or II.

That is, the super-sensitized photographic silver halide emulsion of the present invention contains, together with a cyanine dye, a quaternary salt of an imidazole represented by the general Formula I or II:

wherein R is a hydrogen atom, an alkyl group, such as, a methyl group, an ethyl group and a propyl group or a hydroxyalkyl group, each of R and R is an alkyl group, such as, a methyl group, an ethyl group, and a propyl group, an aralkyl group, such as, a benzyl group, a hydroxyalkyl group, such as, a Z-acetoxyethyl group and a 3-acetoxypropyl group, an aryl group, or an alkenyl group, such as, a vinyl group and an allyl group, R is an alkyl group, such as, a methyl group, an ethyl group and a propyl group, a substituted alkyl group, such as, a B-hydroxylethyl group, 2-acetoxyethyl group, a 3-acetoxypropyl group, an ethylsulfate group, a 2 carboxyethyl group, a 3-carboxypropyl group, a 2-(2-carboxyethoxy) ethyl group, a 2-sulfoethyl group, a 3-sulfopropyl group, a 4-sulfobutyl group, a Z-hydroxy-B-sulfopropyl group, a 2-[2-(3-sulfopropoxy)ethoxy] ethyl group, and a 2-hydroxy-3-(3'-sulfopropoxy)propyl group. Further, X is an anion, such as, a halogen atom, perchloric acid, p-toluenesulfonic acid, ethyl sulfate and thiocyanic acid, m is a positive integer from 2 to 10, n is 1 or 2, and each of Y and Y is a hydrogen atom, an alkyl group, such as, a methyl group and an ethyl group, or a halogen atom, such as, a chlorine atom, a bromine atom or a fluorine atom. Y and Y may form a benzene nucleus or a naphthalene nucleus and the benzene or naphthalene nuclei may be substituted.

DETAILED DESCRIPTION OF THE INVENTION Almost all of the cyanine dyes which are super-sensitized by the quaternary salt of imidazole show the second sensitization maximum (H-band or J-band) under some conditions as, for example, when an emulsion is maintained at a high temperature for a long period of time. The quaternary salt of an imidazole is considered to improve the second sensitization maximum. A silver halide emulsion containing a sensitizing cyanine dye together with the quaternary salt of imidazole to be used in this invention has improved sensitivity at a definite wavelength range. For example, it may have an improved red-sensitivity or yellow-sensitivity, but the formation of fog is scarcely increased in such emulsions. Among the emulsions, there are ones showing reduced fog formation and high super-sensitizing action. See Table 2 in the example.

Several examples of sensitizing cyanine dyes used in this invention are illustrated below, although the invention is not limited to them.

(I) 3,3 diethyl 5,5,9 trimethylselenacarbocyanine bromide;

(II) Anhydro 3,3 di(3 sulfopropyl) 5,5 dichloro-9-ethylthiacarbocyanine hydroxide;

(III) Anhydro 3,3 di(3 sulfopropyl) 4,5,4,5- dibenzothiacarbocyanine hydroxide;

(IV) Anhydro 3,3 di(2 sulfoethyl) 5,5 diphenyl-9-ethyloxacarbocyanine hydroxide;

(V) Anhydro 3,3 di(2 carboxyethyl) 5,5 diphenyl-9-ethyloxacarbocyanine hydroxide;

(VI) 5,5 dichloro 1,l,3,3 tetraethylbenzimidazolocarbocyanine iodide;

(VII) 5,5 dichloro 1,1 diethyl 3,3 di 3- carbovypropylbenzimidazolocarbocyanine bromide;

(VIII) 5,5',6,6' tetrachloro 1,l,3,3 tetraethylbenzimidazolocarbocyanine iodide;

(IX) Anhydro 5,5,6,6-tetrachloro-l,l,3-triethyl-3'- (3 sulfopropyl)-benzimidazolocarbocyanine hydroxide;

(X) Anhydro 5,5',6,6-tetrachloro 1,1 diethyl- 3,3 di[2 [2(3 sulfopropyl)ethoxy]lethylimidazolo- (XI) 5,5',6,6' tetrachloro 1,1,3,3' tetraethylbenzimidazolodicarbocyanine iodide;

(XII) 5,5,6,6 tetrachloro 1,1 diethyl 3,3- di(n-butyl)-benzimidazolodicarbocyanine bromide; and

(XIII) Anhydro 5,5,6,6 tetrachloro 1,1 diethyl- 3,3' di(3 sulfopropyl)benzimidazolocarbocyanine hydroxide.

The quaternary salts of imidazoles used in this invention may be prepared by a well known method and the several examples thereof are as follows:

METHOD 1 Preparation of 1-allyl-2-methyl-3-carboxymethylimidazolium chloride:

CH CH=C g CI'IQCOOH A mixture of g. of 1-allyl-2-methylimidazole and 4.8 g, of chloroacetic acid was heated for 5 hours at 150 C. After the addition of isopropanol, the resulting mixture was stirred and cooled to crystallization. The product thus formed was recrystallized from isopropanol to provide 5 g. of the desired chloride having a melting point of l34136 C.

4 METHOD 2 Preparation of 1 ethyl-2-methyl-3-carboxymethyl-5- chlorobenzimidazolium chloride:

CZH5 1'q\ C-GHs N or- CILCOOH A mixture of 5 g. of l-ethyl-2-methyl-5-chlorobenzimidazole and 3 g. of chloroacetic acid was heated for 2 hours at 150 C. After cooling and washing with acetone,

the product thus obtained was recrystallized from hot water to provide 6 g. of the crystal of the desired chloride having a melting point of 303 C.

METHOD 3 Preparation of 1-ethyl-2-rnethyl-3-carboxymethylbenzimidazolium chloride:

C-CII; Cl-

| CHzCOOH (3) A mixture of 5 g. of l-ethyl-2-methylbenzimidazole and 3.5 g. of chloroacetic acid was heated for 5 hours at 150 C. The product was cooled with the addition of acetone and the crystal deposited was separated by filtration and recrystallized from isopropanol to provide 4 g. of the crystal of the desired chloride having a melting point of 250 C.

METHOD 4 Preparation of 1-ethyl-2-methyl-3-(3-carboxypropyl)- 5,6-chlorobenzimidazolium bromide:

CHzCHzCHzCOOH (4) A mixture of 5 g. of l-ethyl-2-methyl-5,6-dichlorobenzimidazole and 3,6 g. of 'y-bromobutyronitrile was heated for 3 hours to C. by cooling the product and washing it with acetone, 8 g. of a crystal having a melting point of 278279 C., was obtained. A mixture 6 g. of the product, 18 ml. of hydrobromic acid, and 10 ml. of water was boiled under refluxing for 8 hours and the product was cooled with the addition of water to deposit a crystal, which was recovered by filtration and recrystallized from methanol-isopropanol to provide 55 g. of the crystal having a melting point of 258 C.

METHOD 5 Preparation of 1,3-diethyl-2-methyl-5-chlorobenzimidazolium perchlorate:

C-CHg (51* i 2 5 ClOl' (5) A mixture of g. of 1-ethyl-Z methyl-S-chlorobenzimidazole and 4.5 g. of diethyl sulfate was heated for one hour at 100 C. After cooling and washing with ether, the product was dissolved in water by heating and the solution was mixed with an aqueous solution of sodium perchlorate to deposit a crystal, which was recovered by filtration after cooling, washed with water and recrystallized from methanol to provide 7 g. of the crystal having the melting point of 228 C.

METHOD 6 Preparation of 1-ethy1-2-methyl-3-(2-carboxyethyl)-5,6- dichlorobenzimidazolium bromide:

A mixture of 5 g. of 1-ethyl-2-methyl-5,6-dichlorobenzimidazole and 3.3 g. of S-bromopropionamide was heated for 4 hours to 150 C. The product was cooled and washed with acetone to provide 8 g. of a crystal having a melting point of 232-233 C. A mixture of 8 g. of the product, 40 In]. of 48% hydrobromic acid, and 32 ml. of water was boiled for 4 hours under refluxing and the resulting product was cooled, recovered by filtration and recrystallized from methanol-isopropanol to provide 6 g. of the crystal of the objective amide having a melting point of 260 C.

Besides the aforesaid examples of quaternary salts of imidazoles useful in this invention, there are illustrated the following compounds which can also be used:

(7) 1,3 diethyl 2 methyl'benzimidazolium iodide, M.P.

(8) 1,3 diethyl 2 methylbenzimidazolium perchlorate,

M.P. 175-176 C.

(9) Anhydro-1-ethyl-2-methyl-3-(3-sulfopropyl)benzimidazolium hydroxide M.P. 282-283 C.

(10) 1,3-diethyl-2-methyl-S-chlorobenzirnidazolium iodide M.P. 253 C.

(11) Anhydro 1 ethyl 2 methyl 3-(3-sulfopropyl)-5- chlorobenzimidazolium hydroxide M.P. 303 C.

(12) 1-ethyl-2-methy1-3-carboxymethyl-S-chlorobenzimidazolium bromide M.P. 303-304 C.

( 13 1-ethyl-2-methyl-3-carboxymethyl-5-chlorobenz1m1dazolium perchlorate M.P. 217-2 19 C. l4) l-ethyl-2-methyl-3- 2-carboxyethyl) -5-chlorobenz1midazolium bromide M.P. 236237 C. (15 1-ethy1-2-methyl-3-(Z-carboxyethyl) -5-chlorobenz1midazolium perchlorate M.P. 165-167 C.

( 16) 1-ethyl-2-methyl-3-(3-carboxypropyl)-5-chlorobenzimidazolium bromide M.P. 203-204 C.

( 17) 1-ethyl-2-methyl-3-( 3-carboxypropyl)-5-chlorobenzimidazolium perchlorate M.P. 123-125 C.

( 18) Anhydro-1-ethyl-2-methyl-3-(3-sulfopropyl) 5,6-d1- chlorobenzimidazolium hydroxide M.P. 300 C.

(19) 1,3-diethyl-2-methy1-5,6-dichlorobenzimidazolium iodide M.P. 273 C.

(20) 1,3-diethyl-2-methyl-S-cyanobenzimidazolium iodide M.P. 260 C.

(21) 1,3-diethyl-2-methyl 5 cyanobenzimidazolium perchlorate M.P. 237-239 C.

(22) 1-ethyl-2-methyl 3 (Z-hydroxyethyl) -5,6-dichloro benzimidazolium bromide M.P. 286 C.

(23) 1-vinyl-2-methyl-3-methylimidazoliun1 p-toluene sulfonate M.P. 147l49 C.

(24) 1-vinyl-2-methyl-3-benzylimidazolium chloride M.P.

(25) 1-vinyl-2-(2-hydroxyethyl) 3-methyl-4-methylimidazolium-p-toluene sulfonate M.P. 123 C.

(26) 1-vinyl-2-methyl 3 methyl-4-methylimidazolium ptoluene sulfonate M.P. C.

(27) 1-phenyl-2-methy1- 3-ethy1-5,6-dichlorobenzimidazolium p-toluene sulfonate M.P. 228230 C.

(28) 1-benzy1-3-ethyl-benzimidazolium iodide M.P. 173.5-

(29) 1,3-diethylbenzimidazolium iodide M.P. 225227 C.

(30) 1-methyl-3-allyl-5-chloroimidazolium bromide M.P.

(31) 1,3-dimethyl-2-ethylbenzimidazolium iodide M.P.

(32) 3,3 trimethylenebis(1-ethyl-2-methyl-S-chlorobenzimidazolium)perchlorate M.P. 254-256" C.

(33) 3,3 trimethylene'bis(1-ethyl-Z-methyl-5-chlorobenzimidazolium)bromide M.P. 271-272 C.

(34) 1,3-diethyl-2-methyl 4,5 benzobenzimidazolium iodide M.P. 215-217 C.

The suitable concentration of the sensitizing dye used in this invention in a silver halide emulsion is preferably 0.0l-0.2 g. per gram molecule of the silver halide and the suitable concentration of the quaternary salt of imidazole in the emulsion is preferably 0.05-10 g. per gram molecule of silver halide. The concentration ratio of the sensitizing dye to the quaternary salt of imidazole is from about 1:3 to 1:200, and preferably from about 1:10 to 1:100.

The sensitizing dye may be incorporated in the silver halide emulsion in a manner well known in the field. The quaternary salt of imidazole may be incorporated to the silver halide emulsion as a solution in an organic solvent such as methanol or ethanol.

It is convenient to add the sensitizing cyanine dye and the quaternary salt of imidazole used in this invention to a silver halide emulsion directly before coating. In the case of adding them to the emulsion, the sensitizing dye may be added before the addition of the quaternary salt of imidazole or vice versa, or they may be added to the emulsion simultaneously as a mixture thereof.

As the emulsion used in this invention may be used an emulsion containing various silver salts such as silver bromide, silver iodide, silver iodobromide, silver chlorobromide, and silver chloriodo bromide.

The silver halide emulsion of this invention can be applied to a support such as a glass plate, a cellulose derivative film, a synthetic resin film, or a baryta-coated paper by a conventionally adopted manner to provide a photographic light-sensitive material.

The practice of the invention will be apparent by reference to the following example:

EXAMPLE A silver iodobromide emulsion of a batch containing a sensitizing dye, and a silver iodobromide emulsion of the same batch containing the sensitizing dye and also containing quaternary salt of an imidazole were each applied to cellulose acetate film bases separately. The light-sensitive film thus prepared was after exposed through Fuji No. 7, Filter (passing light having wave length longer than 590 m or through Fuji No. 3 Filter (passing light have wave length longer than 490 me) and then developed in a de veloper having the composition shown in Table 1 and the red sensitivity or the yellow sensitivity thereof was measured respectively together with fogs. The results are shown in Table 2.

Table 1.Developer composition G. N-methyl-p-eminophenol sulfate 2.0 Hydroquinone 5.0 Sodium sulfite Borax 2.0

Water to make 1000 ml.

TABLE 2 Quaternary salt of imidazolo (mg./ gram mol of silver halide sensitizing y sJ gram moi of silver halide Sensitivity Red Yellow Emulsion No.2

What we claim is:

1. A photographic silver halide emulsion containing a sensitizing cyanine dye selected from the group consisting of carbocyanine having a nucleus selected from the group consisting of a benzoselenazole, benzothiazole, dibenzothiazole, benzoxazole, benzimidazole and imidazole nucleus, and at least one quaternary salt of an imidazole selected from the group of iinidazoles consisting of those represented by the following general Formulae I and II:

wherein R is selected from the group consisting of a hydrogen atom, an alkyl group and a hydroxyalkyl group, R and R each is a group selected from the group consisting of an alkyl group, an aralkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an aryl group and an alkenyl group, R is selected from the group consisting of an alkyl group and a substituted alkyl group, wherein said substituted alkyl group is selected from the class consisting of an alkyl group substituted with a hydroxyl group, an alkoxy group, an alkyl group substituted with a carboxyl group, an alkyl group substituted with a sulfo group and an alkyl group substituted with a sulfate group, X is an anion, m is an integer from 2 to 10, n is 1 or 2, Y and Y each is a group selected from the group consisting of a hydrogen atom, an alkyl group, a halogen atom and groups which together form a nucleus selected from the group consisting of benzene and naphthalene nuclei and when n is l the compound which has Formula I forms an intermolecular salt wherein R is a group linking an anion introduced from the substituted alkyl group defined above.

2. The emulsion of claim 1 wherein from 0.01 to 0.2 gram of said sensitizing dye per gram molecule of the silver halide in said silver halide emulsion is utilized, and from 0.05 to 10 grams of said quaternary salt of imidazole per gram molecule of silver halide in said silver halide emu1- sion is utilized.

3. The emulsion of claim 2 wherein the ratio of said sensitizing dye to said quaternary salt of imidazole is from about 1:3 to 1:200.

4. The emulsion of claim 3 wherein said ratio is about 1:10 to 1:100.

5. The emulsion of claim 3 wherein said quaternary salt of imidazole is selected from the group consisting of l-allyl-2-methyl-3-carboxymethylimidazolium chloride, l-ethyl-2-methyl-3-carboxymethyl-5-chlorobenzimidazolium chloride, l-ethyl-2-methyl-3-carboxymethylbenzimidazolium chloride, l-ethyl-2-methyl-3-(3-carboxypropyl)-5,6-chlorobenzimidazolium bromide, 1,3-diethyl-Z-methyl-S-chlorobenzimidazolium perchlorate, 1-ethyl-2-methyl-3-(Z-carboxyethyl)-5,6-dichlorobenzimidazolium bromide, 1,3-diethyl-Z-methylbenzimidazolium iodide, 1,3-diethyl-2-methylbenzimidazolium perchlorate, anhydro-1-ethyl-2-methyl-3-(3-sulfopropyl) benzimidazolium hydroxide, l,3-diethyl-2-methyl-5-chlorobenzimidazolium iodide, anhydro-l-ethyl-2-methyl-3-(3-sulfopropyl)-5- chlorobenzimidazolium hydroxide, 1-ethyl-2-methyl-3-carboxymethyl-5-chlorobenzimidazolium bromide, 1-ethyl-2-methyl-3-carboxymethyl-5-chlorobenzimidazolium perchlorate, l-ethyl-2-methyl-3-(Z-carboxyethyl)-5-chlorobenzimidazolium bromide, l-ethyl-2-methyl-3-(Z-carboxyethyl)-5-chlorobenzimidazolium perchlorate, l-ethyl-2-methyl-3- 3-carboxyp ropyl -5-chlorobenzimidazolium bromide, l-ethyl-2-methyl-3- 3-carboxypropyl) -5-chloroben imidazolium perchlorate, anhydrol-ethyl-2-methyl-3- 3-sulfopr0pyl) -5,6-dichlorobenzimidazolium hydroxide, l,3-diethyl-2-methyl-5,6-dichlorobenzimidazolium iodide, l,3-diethyl-2-methyl-S-cyanobenzimidazolium iodide, 1,3-diethyl-2-methyl-S-cyanobenzimidazolium perchlorate, 1-ethyl-2-methyl-3-(2-hydroxyethyl)-5,6-dichlorobenzimidazolium bromide, 1-vinyl-2-methyl-3-rnethylimidazolium p-toluene sulfonate, l-vinyl-2-methyl-3-benzylimidazolium chloride, 1-vinyl-2- Z-hydroxyethyl -3-methyl-4-methylimidazolium-p-toluene sulfonate, l-vinyl-Z-methyl-3-methyl-4-methylimidazolium p-toluene sulfonate, l-phenyl-2-methyl-3-ethyl-5,6-dichlorobenzimidazolium p-toluene sulfonate, l-benzyl-3-ethyl-benzimidazolium iodide, 1,3-diethylbenzimidazolium iodide, 1-methy1-3-allyl-5-chloroimidazolium bromide, l,3-dimethyl-2-ethylbenzimidazolium iodide, 3,3'-trimethylenebis 1-ethyl-2-methyl-S-chlorobenzimidazolium) perchlorate, 3,3-trimethylenebis 1-ethyl-2-methyl-5-chlorobenzimidazolium)bromide, and 1,3-diethyl-2methyl-4,5-benzobenzimidazolium iodide.

6. The emulsion of claim 1 wherein R is an alkyl group of l to 3 carbon atoms, each of R and R is selected from the group consisting of an alkyl group having 1 to 3 carbon atoms, a benzyl group, an acetoxyethyl group, an

acetoxypropyl group, a vinyl group and an allyl group, R is selected from the group consisting of a 1 to 3 carbon atom alkyl group, and a substituted alkyl group selected from the class consisting of a ,B-hydroxyethyl group, a 2-acetoxyethyl group, a 3-acetoxypropyl group, an ethylsulfate group, a 2-carboxyethyl group, a 3-carboxypropyl group, a 2-(2-carboxyethoxy) ethyl group, a 2-su1foethyl group, a 3-sulfopropyl group, a 4-sulfobutyl group, a 2-hydroxy-3-sulfopropyl group, a 2-[2-(3-sulfopropoxy)ethoxy] ethyl group, and a 2-hydroXy-3-(3- sulfopropoxy)propyl group, X is selected from the group consisting of a halogen atom, perchloric acid, p-toluene sulfonic acid, ethylsulfate and thiocyanic acid, and Y and Y are selected from the group consisting of an alkyl group having 1-2 carbon atoms, a chlorine atom, a bromine atom and fluorine atom.

7. A photographic silver halide emulsion as in claim 1 containing a sensitizing cyanine dye selected from the group consisting of carbocyanine having a nucleus selected from the group consisting of a benzoselenazole, benzothiazole, dibenzothiazole, benzoxazole, benzirnidazole and imidazole nucleus, and at least one quaternary salt of an imidazole selected from the group of imidazoles consisting of those represented by the following general formula:

wherein R is selected from the group consisting of a hydrogen atom, an alkyl group and a hydroxyalkyl group, R is a group selected from the group consisting of an alkyl group, an aralkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an aryl group and an alkenyl group, R is selected from the group consisting of an alkyl group and a substituted alkyl group, wherein said substituted alkyl group is selected from the class consisting of an alkyl group substituted with a hydroxyl group, an alkoxy group, an alkyl group substituted with a carboxyl group, an alkyl group substituted with a sulfo group and an alkyl group substituted with a sulfate group, X is an anion, n is 1 or 2, Y and Y each is a group selected from the group consisting of a hydrogen atom, an alkyl group, a halogen atom and groups which together form a nucleus selected from the group consisting of benzene and naphthalene nuclei and when n is l the salt forms an intermolecular salt wherein R is a group linking an anion introduced from the substituted alkyl group defined above.

8. The emulsion of claim 7 wherein from 0.01 to 0.2 gram of said sensitizing dye per gram molecule of the silver halide in said silver halide emulsion is utilized, and from 0.05 to 10 grams of said quaternary salt of imidazole per gram molecule of silver halide in said silver halide emulsion is utilized.

wherein R is selected from the group consisting of a hydrogen atom, an alkyl group and a hydroxyalkyl group, R is a group selected from the group consisting of an alkyl group, an aralkyl group, a hydroxyalkyl group, an acetoxyalkyl group, an aryl group and an alkenyl group, X is an anion, m is an integer from 2 to 10, and Y and Y each is a group selected from the group consisting of a hydrogen atom, an alkyl group, a halogen atom and groups which together form a nucleus selected from the group consisting of benzene and naphthalene nuclei. t

11. The emulsion of claim 10 wherein from 0.01 to 0.2 gram of said sensitizing dye per gram molecule of the silver halide in said silver halide emulsion is utilized, and from 0.05 to 10 grams of said quaternary salt of imidazole per gram molecule of silver halide in said silver halide emulsion is utilized.

12. The emulsion of claim 11 wherein the ratio of said sensitizing dye to said quaternary salt of imidazole is from about 1:3 to 1:200.

References Cited UNITED STATES PATENTS 2,271,623 2/1942 Carroll 96-104 2,288,226 6/1942 Carroll et al. 96104 2,334,864 11/1943 Carroll et al. 96104 2,566,167 8/1951 Carroll et a1, 96-104 2,848,329 8/1958 Chechak et al 96-104 J. TRAVIS BROWN, Primary Examiner 

